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class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Webpack</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Node.js</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>性能优化</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>手写代码</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <main class="page"> <div class="theme-default-content content__default"><h1 id="面试官-说说对css预编语言的理解-有哪些区别"><a href="#面试官-说说对css预编语言的理解-有哪些区别" class="header-anchor">#</a> 面试官：说说对Css预编语言的理解？有哪些区别?</h1> <p><img src="https://static.vue-js.com/81cca1c0-a42c-11eb-85f6-6fac77c0c9b3.png" alt=""></p> <h2 id="一、是什么"><a href="#一、是什么" class="header-anchor">#</a> 一、是什么</h2> <p><code>Css</code> 作为一门标记性语言，语法相对简单，对使用者的要求较低，但同时也带来一些问题</p> <p>需要书写大量看似没有逻辑的代码，不方便维护及扩展，不利于复用，尤其对于非前端开发工程师来讲，往往会因为缺少 <code>Css</code> 编写经验而很难写出组织良好且易于维护的 <code>Css</code> 代码</p> <p><code>Css</code>预处理器便是针对上述问题的解决方案</p> <h4 id="预处理语言"><a href="#预处理语言" class="header-anchor">#</a> 预处理语言</h4> <p>扩充了 <code>Css</code> 语言，增加了诸如变量、混合（mixin）、函数等功能，让 <code>Css</code> 更易维护、方便</p> <p>本质上，预处理是<code>Css</code>的超集</p> <p>包含一套自定义的语法及一个解析器，根据这些语法定义自己的样式规则，这些规则最终会通过解析器，编译生成对应的 <code>Css</code> 文件</p> <h2 id="二、有哪些"><a href="#二、有哪些" class="header-anchor">#</a> 二、有哪些</h2> <p><code>Css</code>预编译语言在前端里面有三大优秀的预编处理器，分别是：</p> <ul><li>sass</li> <li>less</li> <li>stylus</li></ul> <h3 id="sass"><a href="#sass" class="header-anchor">#</a> sass</h3> <p>2007 年诞生，最早也是最成熟的 <code>Css</code>预处理器，拥有 Ruby 社区的支持和 <code>Compass</code> 这一最强大的 <code>Css</code>框架，目前受 <code>LESS</code> 影响，已经进化到了全面兼容 <code>Css</code> 的 <code>Scss</code></p> <p>文件后缀名为<code>.sass</code>与<code>scss</code>，可以严格按照 sass 的缩进方式省去大括号和分号</p> <h3 id="less"><a href="#less" class="header-anchor">#</a> less</h3> <p>2009年出现，受<code>SASS</code>的影响较大，但又使用 <code>Css</code> 的语法，让大部分开发者和设计师更容易上手，在 <code>Ruby</code>社区之外支持者远超过 <code>SASS</code></p> <p>其缺点是比起 <code>SASS</code>来，可编程功能不够，不过优点是简单和兼容 <code>Css</code>，反过来也影响了 <code>SASS</code>演变到了<code>Scss</code> 的时代</p> <h3 id="stylus"><a href="#stylus" class="header-anchor">#</a> stylus</h3> <p><code>Stylus</code>是一个<code>Css</code>的预处理框架，2010 年产生，来自 <code>Node.js</code>社区，主要用来给 <code>Node</code> 项目进行 <code>Css</code> 预处理支持</p> <p>所以<code>Stylus</code> 是一种新型语言，可以创建健壮的、动态的、富有表现力的<code>Css</code>。比较年轻，其本质上做的事情与<code>SASS/LESS</code>等类似</p> <h2 id="三、区别"><a href="#三、区别" class="header-anchor">#</a> 三、区别</h2> <p>虽然各种预处理器功能强大，但使用最多的，还是以下特性：</p> <ul><li>变量（variables）</li> <li>作用域（scope）</li> <li>代码混合（ mixins）</li> <li>嵌套（nested rules）</li> <li>代码模块化（Modules）</li></ul> <p>因此，下面就展开这些方面的区别</p> <h3 id="基本使用"><a href="#基本使用" class="header-anchor">#</a> 基本使用</h3> <p>less和scss</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token selector">.box</span> <span class="token punctuation">{</span>
  <span class="token property">display</span><span class="token punctuation">:</span> block<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p>sass</p> <div class="language-Css extra-class"><pre class="language-css"><code>.box
  <span class="token property">display</span><span class="token punctuation">:</span> block
</code></pre></div><p>stylus</p> <div class="language-Css extra-class"><pre class="language-css"><code>.box
  <span class="token property">display</span><span class="token punctuation">:</span> block
</code></pre></div><h3 id="嵌套"><a href="#嵌套" class="header-anchor">#</a> 嵌套</h3> <p>三者的嵌套语法都是一致的，甚至连引用父级选择器的标记 &amp; 也相同</p> <p>区别只是 Sass 和 Stylus 可以用没有大括号的方式书写</p> <p>less</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token selector">.a</span> <span class="token punctuation">{</span>
  <span class="token selector">&amp;.b</span> <span class="token punctuation">{</span>
    <span class="token property">color</span><span class="token punctuation">:</span> red<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
<span class="token punctuation">}</span>
</code></pre></div><h3 id="变量"><a href="#变量" class="header-anchor">#</a> 变量</h3> <p>变量无疑为 Css 增加了一种有效的复用方式，减少了原来在 Css 中无法避免的重复「硬编码」</p> <p><code>less</code>声明的变量必须以<code>@</code>开头，后面紧跟变量名和变量值，而且变量名和变量值需要使用冒号<code>:</code>分隔开</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token atrule"><span class="token rule">@red</span><span class="token punctuation">:</span> #c00<span class="token punctuation">;</span></span>

<span class="token selector">strong</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span> <span class="token atrule"><span class="token rule">@red</span><span class="token punctuation">;</span></span>
<span class="token punctuation">}</span>
</code></pre></div><p><code>sass</code>声明的变量跟<code>less</code>十分的相似，只是变量名前面使用<code>@</code>开头</p> <div class="language-Css extra-class"><pre class="language-css"><code>$<span class="token property">red</span><span class="token punctuation">:</span> #c00<span class="token punctuation">;</span>

<span class="token selector">strong</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span> $red<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p><code>stylus</code>声明的变量没有任何的限定，可以使用<code>$</code>开头，结尾的分号<code>;</code>可有可无，但变量与变量值之间需要使用<code>=</code></p> <p>在<code>stylus</code>中我们不建议使用<code>@</code>符号开头声明变量</p> <div class="language-Css extra-class"><pre class="language-css"><code>red = #c00

strong
  <span class="token property">color</span><span class="token punctuation">:</span> red
</code></pre></div><h3 id="作用域"><a href="#作用域" class="header-anchor">#</a> 作用域</h3> <p><code>Css</code> 预编译器把变量赋予作用域，也就是存在生命周期。就像 <code>js</code>一样，它会先从局部作用域查找变量，依次向上级作用域查找</p> <p><code>sass</code>中不存在全局变量</p> <div class="language-Css extra-class"><pre class="language-css"><code>$<span class="token property">color</span><span class="token punctuation">:</span> black<span class="token punctuation">;</span>
<span class="token selector">.scoped</span> <span class="token punctuation">{</span>
  $<span class="token property">bg</span><span class="token punctuation">:</span> blue<span class="token punctuation">;</span>
  $<span class="token property">color</span><span class="token punctuation">:</span> white<span class="token punctuation">;</span>
  <span class="token property">color</span><span class="token punctuation">:</span> $color<span class="token punctuation">;</span>
  <span class="token property">background-color</span><span class="token punctuation">:</span>$bg<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.unscoped</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span>$color<span class="token punctuation">;</span>
<span class="token punctuation">}</span> 
</code></pre></div><p>编译后</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token selector">.scoped</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span>white<span class="token punctuation">;</span><span class="token comment">/*是白色*/</span>
  <span class="token property">background-color</span><span class="token punctuation">:</span>blue<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.unscoped</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span>white<span class="token punctuation">;</span><span class="token comment">/*白色（无全局变量概念）*/</span>
<span class="token punctuation">}</span> 
</code></pre></div><p>所以，在<code>sass</code>中最好不要定义相同的变量名</p> <p><code>less</code>与<code>stylus</code>的作用域跟<code>javascript</code>十分的相似，首先会查找局部定义的变量，如果没有找到，会像冒泡一样，一级一级往下查找，直到根为止</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token atrule"><span class="token rule">@color</span><span class="token punctuation">:</span> black<span class="token punctuation">;</span></span>
<span class="token selector">.scoped</span> <span class="token punctuation">{</span>
  <span class="token atrule"><span class="token rule">@bg</span><span class="token punctuation">:</span> blue<span class="token punctuation">;</span></span>
  <span class="token atrule"><span class="token rule">@color</span><span class="token punctuation">:</span> white<span class="token punctuation">;</span></span>
  <span class="token property">color</span><span class="token punctuation">:</span> <span class="token atrule"><span class="token rule">@color</span><span class="token punctuation">;</span></span>
  <span class="token property">background-color</span><span class="token punctuation">:</span><span class="token atrule"><span class="token rule">@bg</span><span class="token punctuation">;</span></span>
<span class="token punctuation">}</span>
<span class="token selector">.unscoped</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span><span class="token atrule"><span class="token rule">@color</span><span class="token punctuation">;</span></span>
<span class="token punctuation">}</span> 
</code></pre></div><p>编译后：</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token selector">.scoped</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span>white<span class="token punctuation">;</span><span class="token comment">/*白色（调用了局部变量）*/</span>
  <span class="token property">background-color</span><span class="token punctuation">:</span>blue<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.unscoped</span> <span class="token punctuation">{</span>
  <span class="token property">color</span><span class="token punctuation">:</span>black<span class="token punctuation">;</span><span class="token comment">/*黑色（调用了全局变量）*/</span>
<span class="token punctuation">}</span> 
</code></pre></div><h3 id="混入"><a href="#混入" class="header-anchor">#</a> 混入</h3> <p>混入（mixin）应该说是预处理器最精髓的功能之一了，简单点来说，<code>Mixins</code>可以将一部分样式抽出，作为单独定义的模块，被很多选择器重复使用</p> <p>可以在<code>Mixins</code>中定义变量或者默认参数</p> <p>在<code>less</code>中，混合的用法是指将定义好的<code>ClassA</code>中引入另一个已经定义的<code>Class</code>，也能使用够传递参数，参数变量为<code>@</code>声明</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token selector">.alert</span> <span class="token punctuation">{</span>
  <span class="token property">font-weight</span><span class="token punctuation">:</span> 700<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

.<span class="token function">highlight</span><span class="token punctuation">(</span><span class="token atrule"><span class="token rule">@color</span><span class="token punctuation">:</span> red<span class="token punctuation">)</span></span> <span class="token punctuation">{</span>
  <span class="token property">font-size</span><span class="token punctuation">:</span> 1.2em<span class="token punctuation">;</span>
  <span class="token property">color</span><span class="token punctuation">:</span> <span class="token atrule"><span class="token rule">@color</span><span class="token punctuation">;</span></span>
<span class="token punctuation">}</span>

<span class="token selector">.heads-up</span> <span class="token punctuation">{</span>
  .alert<span class="token punctuation">;</span>
  .<span class="token function">highlight</span><span class="token punctuation">(</span>red<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p>编译后</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token selector">.alert</span> <span class="token punctuation">{</span>
  <span class="token property">font-weight</span><span class="token punctuation">:</span> 700<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.heads-up</span> <span class="token punctuation">{</span>
  <span class="token property">font-weight</span><span class="token punctuation">:</span> 700<span class="token punctuation">;</span>
  <span class="token property">font-size</span><span class="token punctuation">:</span> 1.2em<span class="token punctuation">;</span>
  <span class="token property">color</span><span class="token punctuation">:</span> red<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p><code>Sass</code>声明<code>mixins</code>时需要使用<code>@mixinn</code>，后面紧跟<code>mixin</code>的名，也可以设置参数，参数名为变量<code>$</code>声明的形式</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token atrule"><span class="token rule">@mixin</span> large-text</span> <span class="token punctuation">{</span>
  <span class="token selector">font:</span> <span class="token punctuation">{</span>
    <span class="token property">family</span><span class="token punctuation">:</span> Arial<span class="token punctuation">;</span>
    <span class="token property">size</span><span class="token punctuation">:</span> 20px<span class="token punctuation">;</span>
    <span class="token property">weight</span><span class="token punctuation">:</span> bold<span class="token punctuation">;</span>
  <span class="token punctuation">}</span>
  <span class="token property">color</span><span class="token punctuation">:</span> #ff0000<span class="token punctuation">;</span>
<span class="token punctuation">}</span>

<span class="token selector">.page-title</span> <span class="token punctuation">{</span>
  <span class="token atrule"><span class="token rule">@include</span> large-text<span class="token punctuation">;</span></span>
  <span class="token property">padding</span><span class="token punctuation">:</span> 4px<span class="token punctuation">;</span>
  <span class="token property">margin-top</span><span class="token punctuation">:</span> 10px<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre></div><p><code>stylus</code>中的混合和前两款<code>Css</code>预处理器语言的混合略有不同，他可以不使用任何符号，就是直接声明<code>Mixins</code>名，然后在定义参数和默认值之间用等号（=）来连接</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token selector">error(borderWidth= 2px)</span> <span class="token punctuation">{</span>
  <span class="token property">border</span><span class="token punctuation">:</span> borderWidth solid #F00<span class="token punctuation">;</span>
  <span class="token property">color</span><span class="token punctuation">:</span> #F00<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token selector">.generic-error</span> <span class="token punctuation">{</span>
  <span class="token property">padding</span><span class="token punctuation">:</span> 20px<span class="token punctuation">;</span>
  <span class="token property">margin</span><span class="token punctuation">:</span> 4px<span class="token punctuation">;</span>
  <span class="token function">error</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">/* 调用error mixins */</span>
<span class="token punctuation">}</span>
<span class="token selector">.login-error</span> <span class="token punctuation">{</span>
  <span class="token property">left</span><span class="token punctuation">:</span> 12px<span class="token punctuation">;</span>
  <span class="token property">position</span><span class="token punctuation">:</span> absolute<span class="token punctuation">;</span>
  <span class="token property">top</span><span class="token punctuation">:</span> 20px<span class="token punctuation">;</span>
  <span class="token function">error</span><span class="token punctuation">(</span>5px<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token comment">/* 调用error mixins，并将参数$borderWidth的值指定为5px */</span>
<span class="token punctuation">}</span> 
</code></pre></div><h3 id="代码模块化"><a href="#代码模块化" class="header-anchor">#</a> 代码模块化</h3> <p>模块化就是将<code>Css</code>代码分成一个个模块</p> <p><code>scss</code>、<code>less</code>、<code>stylus</code>三者的使用方法都如下所示</p> <div class="language-Css extra-class"><pre class="language-css"><code><span class="token atrule"><span class="token rule">@import</span> <span class="token string">'./common'</span><span class="token punctuation">;</span></span>
<span class="token atrule"><span class="token rule">@import</span> <span class="token string">'./github-markdown'</span><span class="token punctuation">;</span></span>
<span class="token atrule"><span class="token rule">@import</span> <span class="token string">'./mixin'</span><span class="token punctuation">;</span></span>
<span class="token atrule"><span class="token rule">@import</span> <span class="token string">'./variables'</span><span class="token punctuation">;</span></span>
</code></pre></div><h2 id="参考文献"><a href="#参考文献" class="header-anchor">#</a> 参考文献</h2> <ul><li>https://jelly.jd.com/article/5dcb9c73641a030153732a89</li> <li>https://zhuanlan.zhihu.com/p/23382462</li> <li>https://baike.baidu.com/item/Less/17570158</li></ul></div> <footer class="page-edit"><!----> <div class="last-updated"><span class="prefix">更新时间:</span> <span class="time">12/14/2021, 10:12:35 AM</span></div></footer> <div class="page-nav"><p class="inner"><span class="prev">
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